Post-processing apparatus and image forming system

ABSTRACT

A post-processing apparatus having therein a stacker that stocks sheets temporarily and an ejection device that ejects a plurality of sheets stacked on the stacker from the stacker wherein the ejection device has an ejection claw that pushes up the plural sheets and a moving device that moves the ejection claw along the stacker, the ejection claw has a contact surface with which the aforesaid plural sheets are brought into contact when the plural sheets are pushed up, and the contact surface has plural protrusions protruding toward the plural sheets.

This application is based on Japanese Patent Application No. 2007-293003filed on Nov. 12, 2007 in Japanese Patent Office, the entire content ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a post-processing apparatus havingtherein a stacker that stocks sheets temporarily and an ejection devicethat ejects a plurality of sheets stacked on the stacker and to an imageforming system having therein the post-processing apparatus.

There is known a post-processing apparatus wherein plural image-recordedsheets ejected from an image forming apparatus are collected in the formof a group of plural sheets to be outputted, or sheets are collated foreach copy and stapled by a stapler to be outputted.

It is further known that a period of time required for post-processingsuch as stapler processing in a post-processing apparatus is generallylonger than a period of time required for image forming processing in animage forming apparatus.

Therefore, there is known a post-processing apparatus wherein a stackerthat stocks sheets temporarily is provided in the post-processingapparatus to stack a prescribed number of sheets.

As the post-processing apparatus of this kind, there is known anapparatus wherein an ejection device that ejects stacked plural sheetsto an ejection tray and a stapler representing a post-processingapparatus is provided, and plural sheets are pushed up and ejected by anejection claw fixed on the ejection device (for example, UnexaminedJapanese Patent Application Publication No. 8-137151).

In the post-processing apparatus described in Unexamined Japanese PatentApplication Publication No. 8-137151, it is possible to eject pluralsheets (sheet bundle) to an ejection tray or to a stapler, by pushing upplural sheets with an ejection claw provided on the ejection device

However, with respect to a shape of the ejection claw, its contactsurface with a sheet is flat, excluding a protrusion on the uppermostsection, as illustrated in FIG. 1 (a). Therefore, in the case of a poorfragile sheet or a curled sheet, in particular, the contact portion sideof the sheet contacting the ejection claw tends to be shifted toward atip portion of the ejection claw when a sheet bundle is pushed up, andif it is shifted greatly, there is a possibility that the contactportion side of the sheet contacting the ejection claw climbs over theprotrusion on the uppermost section, causing conveyance abnormality,which has been a problem.

Further, for example, when an ejection claw is arranged only at aposition corresponding to the width direction of a small-sized sheet, ifa large-sized sheet is tried to be ejected out, resistance of conveyanceis increased by curls on the end portion of the large-sized sheetbundle, and the sheet is easily skewed. If the sheet is skewed, there isa possibility that the contact portion side of the sheet contacting theejection claw climbs over the protrusion on the uppermost section,causing conveyance abnormality, which has been a problem.

The followings are aspects of the invention.

1. A post-processing apparatus comprising: a stacker which stocks asheet temporarily; and an ejection device which ejects a plurality ofsheets from the stacker on which the plurality of sheets have beenstacked, the ejection device comprising: an ejection claw which pushesup the plurality of sheets; and a moving device which moves the ejectionclaw along the stacker, wherein the ejection claw comprises a contactsurface with which the plurality of sheets are brought into contact whenthe ejection claw moves and pushes up the plurality of sheets by themoving device, and the contact surface comprises a plurality ofprotrusions which protrudes toward the plurality of sheets stacked onthe stacker.2. An image forming system having therein an image forming apparatusthat conducts image forming on a sheet and a post-processing apparatusdescribed in the aforesaid Item 1 connected to the image formingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (a) is a conceptual diagram describing a stacker and an ejectiondevice in a conventional embodiment and FIG. 1 (b) is one in a presentembodiment.

FIG. 2 is a diagram showing a post-processing apparatus and an imageforming system equipped with the post-processing apparatus.

FIGS. 3 (a) and 3 (b) are schematic diagrams showing sheet conveyancecourses including the first conveyance path and the second conveyancepath.

FIG. 4 is a schematic diagram showing a sheet conveyance course usingthe third conveyance path.

Each of FIGS. 5 (a) and 5 (b) is a detailed diagram of an ejection clawfixed on an ejection belt.

Each of FIGS. 6 (a) and 6 (b) is a diagram of another embodiment for aprotrusion provided on an ejection claw.

FIG. 7 is a diagram of the fourth embodiment for a protrusion providedon an ejection claw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Prior to the detailed description of the embodiment, outlines of thepresent embodiment and of the conventional embodiment will be describedas follows, for easy understanding of the description.

FIGS. 1 (a) and 1 (b) are conceptual diagrams describing a stacker andan ejection device in a conventional embodiment and those in a presentembodiment.

FIG. 1 (a) is a conceptual diagram describing a conventional stacker anda conventional ejection device, while, FIG. 1 (b) is a conceptualdiagram describing a stacker and an ejection device both in the presentembodiment.

In FIG. 1 (a), stacker 101 that stacks plural sheets temporarily hasstopper 103 that conducts alignment on the conveyance direction side forsheets fed from the preceding process, whereby, plural sheets arestacked while alignment of sheets on the conveyance direction side isconducted (two-dot chain lines).

Ejection device 102 that ejects a bundle of sheets (two-dot chain lines)stacked on stacker 101 has ejection claw 104 that pushes up bundle ofsheets P1 (solid lines) in the direction of the arrow to eject themtoward the succeeding progress.

Contact surface 105 of ejection claw 104 with which a bundle of sheetsis brought into contact is flat, and tip portion 106 of the ejectionclaw is slightly protrudent in the pushing up direction.

The ejection claw 104 has no measures to prevent a bundle of sheets frombeing shifted on contact surface 105 undesirably toward tip portion 106,and only measures to prevent a bundle of sheets from protruding fromejection claw 104 are represented by tip portion 106 that is slightlyprotrudent in the pushing up direction.

For this reason, when the bundle of sheets is pushed up in the directionof the arrow, its portion on the side of contact with ejection claw 104tends to be bent, as illustrated, and in the case of a non-rigid sheetor in the case of existence of a curl, in particular, there is apossibility that the bundle of sheets is shifted undesirably on thecontact surface 105, and it runs on protrusion 107 on the tip portion.

The foregoing means that the force toward protrusion 107 of a tipportion by own weight of a bundle of sheets overcomes frictional forcebetween the bundle of sheets and contact surface 105, thus, the bundleof sheets is shifted to the protrusion 107 side.

As a result, when the bundle of sheets runs on the protrusion 107 of thetip portion, there is caused conveyance abnormality which has been acause for the decline of reliability and productivity.

In FIG. 1 (b), stacker 111 that stacks plural sheets temporarily hasstopper 113 that conducts alignment on the conveyance direction side forsheets fed from the preceding process, whereby, plural sheets arestacked while alignment of sheets on the conveyance direction side isconducted (two-dot chain lines).

Ejection device 112 that ejects plural sheets (two-dot chain lines)stacked on stacker 111 from stacker 111 by pushing up them has ejectionclaw 114 that pushes up plural sheets, namely, bundle of sheets P1(solid lines) in the direction of the arrow to eject them toward thesucceeding progress, and has ejection belt 56 that is a moving device tomove the ejection claw 114 in the direction for pushing up along stacker111.

Contact surface 115 of ejection claw 114 touched by the bundle of sheetshas protrusions 118, and tip portion 116 of ejection claw 114 formsprotrusion 117 that is taller than the protrusions 118 in the direction(direction of the arrow) for pushing up.

Owing to this, although bundle of sheets P1 tends to be bent when it ispushed up, a contact side of the sheet contacting ejection claw 114(hereafter, a contact side of the sheet contacting ejection claw 114 isdescribed as a trailing edge of the sheet) is caught by protrusions 118.Therefore, the trailing edge of a sheet is restrained from sliding oncontact surface 115 and from being moved toward protrusion 117, even inthe case of existence of curls, in particular, thus, the bundle ofsheets P1 is prevented from being bent greatly.

Therefore, the bundle of sheets P1 can be prevented from running onprotrusion 117 of the aforesaid tip portion.

In other words, the bundle of sheets P1 is caused to be caught by thecontact surface 115 thereon, and thereby, a trailing edge of the bundleof sheets P1 is prevented from being shifted toward the protrusion 117,without relying on frictional force between the bundle of sheets P1 andthe contact surface 115 thereon as in the past.

Owing to this, no conveyance abnormality is caused, and reliability andproductivity are improved.

Referring to the drawings, embodiments will be described as follows, towhich, however, the invention is not limited.

Incidentally, devices and members having the same functions and forms asthose in other drawings are given the same symbols as those in otherdrawings.

FIG. 2 is a diagram showing a post-processing apparatus and an imageforming system equipped with the post-processing apparatus.

Image forming system Z has therein image forming apparatus A thatrecords an image on a sheet and a post-processing apparatus B thatconducts post-processing on the sheet on which the image is recorded bythe image forming apparatus A.

First, the image forming apparatus A will be described.

The image forming apparatus A is one (for example, a copying machine, aprinter and a facsimile machine) that forms an image on a sheet throughan electrophotographic method, and it has image forming section A1,document feeding device A2 and image reading section A3.

Start-up of the image forming apparatus A starts document feeding deviceA2 to operate.

The document feeding device A2 conveys documents to a reading positionone after another.

Then, the image reading section A3 reads a document conveyed by thedocument feeding device A2 or an image of a document placed on documenttable 9, and generates image signals.

Around drum-shaped photoreceptor 1 in the image forming section A1,there are arranged charging unit 2 that charges photoreceptor 1uniformly, exposure unit 3 that gives exposure based on the aforesaidimage signals of an image of the document, developing unit 4 thatvisualizes a latent image resulted from exposure by using toner,transfer unit 5A that transfers a toner image formed on thephotoreceptor onto a sheet, separation unit 5B that separates a sheetfrom photoreceptor 1, and cleaning unit 6 that removes toner remainingon photoreceptor 1, whereby, images are formed on sheet S by these unitsof electrophotographic process.

Sheet S is stored in sheet feed tray 7A, and sheet S is fed from sheetfeed tray 7A one by one, and a toner image on photoreceptor 1 istransferred onto sheet S by transfer unit 5A.

Then, the toner image transferred onto sheet S passes through fixingunit 8 to be subjected to fixing processing.

Then, the sheet S which has been subjected to the fixing processing isejected to post-processing apparatus B from sheet ejection roller 7C.

In the case of two-sided image forming, the sheet S is guided downwardby switching gate 7D, and it passes through sheet re-feed path 7E afterbeing reversed inside out by a switchback, to be fed to transfer unit 5Aagain where an image on the reverse side is transferred.

Operation panel P representing a selection device for selectingoperations of post-processing conducted by post-processing apparatus Bhas a touch panel (not shown), and it displays various selectionswitches and information relating to operations of post-processing onthe touch panel.

For example, selection switches for sizes of sheets to be used such asA4 and B4 and selection switches for operations of post-processing suchas, for example, sheet stacking processing and staple processing, aredisplayed.

Then, various pieces of information from operations of various types ofselection switches are inputted in control device C1.

Each of the image forming apparatus A and the post-processing apparatusB has an information sending and receiving device that sends andreceives post-processing operation information selected by the aforesaidpost-processing operation selecting switch that is a selection devicewhich selects operations of post-processing to be conducted in thepost-processing apparatus.

Communication device C11 of image forming apparatus A conducting serialcommunication and communication device C21 of post-processing apparatusB, both representing an information sending and receiving device sendand receive various types of information relating to operations ofpost-processing each other.

Control device C1 controls the aforesaid operations relating to theimage forming apparatus A.

Post-processing apparatus B will be described as follows.

The post-processing apparatus B is an apparatus for conducting varioustypes of post-processing including staple processing on sheet S fed infrom the image forming apparatus A.

The post-processing apparatus B is installed after its position andheight are adjusted so that an entrance portion for sheet S may agreewith an ejecting direction of ejection roller 7C of image formingapparatus A, and the post-processing apparatus B is driven in accordancewith operations of the image forming apparatus A.

A conveyance path for sheet S that is connected to the downstream sideof the sheet conveyance direction of paired entrance rollers 11 in theaforesaid entrance portion is branched into three ways including firstconveyance path 100 on the upper portion, second conveyance path 200 onthe medium portion and third conveyance path 300 on the lower portion.

Then, sheet S is fed to any one of the conveyance paths through theselection of an angle of each of switching gates G1, G2 and G3.

The first conveyance path 100 causes sheet S to be ejected and stackedon sheet ejection tray 19 located at an upper portion outside theapparatus.

Through the second conveyance path 200, sheet S is ejected and stackedon sheet ejection tray 40 by paired ejection rollers 20.

On the third conveyance path 300, there are provided stacker 51 thatstocks temporarily sheet S and ejection device 60 that pushes up pluralsheets stacked on the stacker 51 to eject them from the stacker 51.

The ejection device 60 has therein ejection claw 57 that pushes upplural sheets and ejection belt 56 representing a moving device thatmoves the ejection claw 57 in the direction to push up the ejection claw57 along the stacker 51.

A bundle of sheets subjected to stapling processing by stapler 50 afterprescribed number of sheets S are stacked on stacker 51, or a bundle ofplural sheets collected on the stacker 51 is pushed up by ejectiondevice 60 to be ejected and stacked on sheet ejection tray 40 by pairedejection rollers 20.

Incidentally, the ejection device 60 has a plurality of ejection belts56, depending on a size of a sheet to be used.

For example, when carrying out post-processing for sheets ranging fromB5 to A3 in terms of a size, one ejection belt 56 is provided near eachof both ends of a B5 sheet size, for post-processing of B5 and A4 sheet,by which B5 and A4 sheets are pushed up. One ejection belt 56 isprovided near each of both ends of a B4 sheet size, for post-processingof B4 and A3 sheet, by which B4 and A3 sheets are pushed up.

Controller C2 controls the aforesaid operations relating topost-processing apparatus B, in accordance with information ofoperations of post-processing received through communication device C21.

Each of FIGS. 3 (a) and 3 (b) is a schematic diagram showing a sheetconveyance course through the first conveyance path and a sheetconveyance course through the second conveyance path.

FIG. 3 (a) shows a conveyance course (one-dot chain lines) for sheet Sthrough the first conveyance path 100, and FIG. 3 (b) shows a conveyancecourse (one-dot chain lines) for sheet S through the second conveyancepath 200.

(1) First Conveyance Path 100 (Printer Mode, Sheet Ejection with anImage Surface Facing Downward)

In FIG. 3 (a), sheet S ejected from image forming apparatus A with animage surface facing upward (face-up) is conveyed by paired entrancerollers 11, then, passes through passage 121 located at a lower part ofupper first switching gate G1, to be interposed between pairedconveyance rollers 12, and passes through passage 123 located at anupper part of second switching gate G2 that is positioned downwardobliquely.

Then, the sheet S passes through paired conveyance rollers 14, passage15 and paired conveyance rollers 16 to stop once.

Then, after stopping once, the sheet S is given an operation of aswitchback by paired conveyance rollers 12, 14 and 16 which rotatereversely, and passes through passage 122 positioned at an upper part ofthe first switching gate G1 and passage 17 located higher (firstconveyance path 100), and is ejected out by paired ejection rollers 18onto sheet ejection tray 19 positioned at an upper part outside theapparatus with its image surface facing downward (face-down), to beplaced in the order of pages.

(2) Second Conveyance Path 200 (Copy Mode, Sheet Ejection with an ImageSurface Facing Upward, Non-Staple Mode Including Offset Ejection)

In FIG. 3 (b), sheet S ejected from image forming apparatus A with animage surface facing upward is conveyed by paired entrance rollers 11,then, passes through passage 121 located at a lower part of upper firstswitching gate G1.

Then, the sheet S is interposed between paired conveyance rollers 12,and passes through passage 123 located at an upper part of secondswitching gate G2 that is positioned downward obliquely, and is ejectedout with its image surface facing upward to be placed in the order ofpages by paired ejection rollers 20 onto sheet ejection tray 40 that islocated outside the apparatus.

FIG. 4 is a schematic diagram showing a sheet conveyance course throughthe third conveyance path.

FIG. 4 shows a conveyance course (one-dot chain lines) for sheet Sthrough the third conveyance path 300.

(3) Third Conveyance Path 300 (Copy Mode, Sheet Ejection with an ImageSurface Facing Upward, Staple Mode)

In FIG. 4, sheets S which have been subjected to image formingprocessing in image forming apparatus A are ejected out in successionwith an image surface facing upward, beginning with a copy of the lastpage.

Sheet S fed into sheet post-processing apparatus B is conveyed by pairedentrance rollers 11, and passes through passage 121 located at a lowerpart of upper first switching gate G1.

Then, the sheet S is interposed between paired conveyance rollers 12,and passes through passage 124 located at an upper part of thirdswitching gate G3 that is positioned downward obliquely, or throughlower passage 125, and is fed in stacker 51 through paired conveyancerollers 41, passage 42 (third conveyance path 300) and paired conveyancerollers 43 positioned at the downstream side of the passage 42.

Sheet S interposed between and conveyed by the paired conveyance rollers43 positioned at the downstream side of the passage 42 is discharged toan upper space of stacker 51 arranged obliquely, and slides and risesfurther while touching stacker 51 or an upper face of a sheet stacked onthe stacker 51.

After sliding and rising, the sheet S starts descending with its ownweight, and slides down along an inclined plane of stacker 51 to stopafter hitting sheet hitting surface (stopper member) 52 near stapler 50.

Rotary blade wheel 44 that assists the sheet S for sliding down hasblades (having no symbol), whereby, when the sheet S is subject to aswitchback, rotating blades are brought into sliding contact with thesheet S, so that the sheet S is caused to touch the stopper member 52surely.

The numeral 53 represents a pair of alignment members provided movablyon both sides of the aforesaid stacker 51.

The paired alignment members 53 are movable in the directionperpendicular to the sheet-conveyance direction.

When sheet S is discharged onto stacker 51, the paired alignment members53 are opened to be broader than a sheet width and when the sheet Sslides down along stacker 51 and hits stopper member 52 to stop, thepaired alignment members 53 move in the direction of the sheet width ona reciprocation basis, and conduct width aligning (alignment) of abundle of sheets by tapping a side edge of sheets S.

After sheets S in prescribed quantity are stacked and aligned on stacker51 at this stopping position, binding processing (staple processing) isconducted by stapler 50 and bundle of stapled sheets S1 is completed.

Even when the staple processing is not conducted, it is also possible toemploy constitution wherein plural sheets S are conveyed to stacker 51for improving accuracy of alignment and, width aligning (alignment) ofbundle of sheets S2 stacked simply is conducted by alignment member 53.

On a part in the width direction of a sheet-stacking surface of stacker51, there is formed a notched portion extending in the directionperpendicular to the width direction, and in this notched portion, thereare arranged plural ejection belts 56 each being wound around drivingpulley 54 and driven pulley 55, so that the plural ejection belts may bedriven to rotate.

On a part of the ejection belt 56, there is fixed ejection claw 57, anda tip portion of the ejection claw 57 moves to draw an oblong locus asshown with illustrated one-dot chain lines.

Bundle of stapled sheets S1 or bundle of plural sheets S2 simply stackedwhich is placed on the ejection belt 56 slides, with its trailing edgeheld by ejection claw 57 of ejection belt 56, along a placement surfaceof stacker 51, to be pushed upward obliquely, and advances to theposition of a nip of paired ejection rollers 20.

Bundle of stapled sheets S1 or bundle of plural sheets S2 simply stackedis interposed between rotating paired ejection rollers 20, to be ejectedand stacked onto sheet ejection tray 40.

Each of FIGS. 5 (a) and 5 (b) is a detailed diagram of the ejection clawfixed on the ejection belt.

Each of FIGS. 5 (a) and 5 (b) is a sectional view of ejection claw 57that is viewed in the same direction as in FIG. 4.

FIG. 5 (a) is a detailed diagram of ejection claw 57 and FIG. 5 (b) is adetailed diagram of a protrusion of the ejection claw 57.

The ejection claw 57 and its protrusions will be described as follows,referring to FIG. 5 (a) and FIG. 5 (b).

The ejection claw 57 is moved by ejection belt 56 in the direction ofarrow E, when bundle of stapled sheets S1 or bundle of plural sheets S2simply stacked (hereafter, bundle of stapled sheets S1 or bundle ofplural sheets S2 simply stacked is described simply as a bundle ofsheets) is ejected.

The ejection claw 57 has therein main body section 58 fixed on ejectionbelt 56 which is the aforesaid moving device, and sheet contact section59 that is fixed on the main body section 58 with an adhesive or thelike and is in contact with by sheets when bundle of sheets S1 or bundleof sheets S2 is pushed up.

The main body section 58 is formed with a resin which is used usually ina post-processing apparatus, and it is fixed on the ejection belt 56with screws or an adhesive.

Sheet contact section 59 has, on its sheet contact surface 591, pluralprotrusions 592 which protrude toward bundle of sheets S1 or bundle ofsheets S2.

The protrusions 592 extend in the direction that is parallel to thewidth direction (the width direction means a direction perpendicular tothe sheet-conveyance direction, that is, the illustration sheetfront-back direction) of a sheet of a bundle of sheets and protrudetoward the bundle of sheets, and for example, they are projections in arectangular form.

It is preferable that width w1 of the aforesaid projection in arectangular form (namely, protrusion 592) is about 1 mm, and height h1is about 0.3 mm.

When the width of the projection is broad, the number of projections isfewer, resulting in fewer portions where sheets are caught. When thewidth of the projection is narrow, strength of protrusion 592 islowered.

When the height of the projection is low, a sheet is hardly caught,while, when the projection is tall, accuracy of alignment in theconveyance direction is deteriorated, and a sheet is more easily hurt atthe corner of the protrusion.

Further, it is preferable that width w2 of recess 595 between adjoiningprotrusions is about 2 mm, and when the width is broad, the number ofprojections is fewer, resulting in fewer portions where sheets arecaught. When the width of the projection is narrow, a sheet is hardlycaught.

At least surface 593 facing ejection belt 56 among both side faces ofthe aforesaid rectangular-shaped projection (namely, protrusion 592) isat prescribed angle θ on the bottom plane of recess 595 betweenadjoining protrusions 592.

It is desirable that the prescribed angle θ is an angle so that thesheet S constituting a bundle of sheets is caught in each protrusion592, and so that a sheet does not get over each of protrusions 592,which is for example, 80°-95°, preferably 90°.

When the prescribed angle θ is greater than 95°, a sheet is hardlycaught by the protrusion 592, and a sheet easily gets over the aforesaidplural protrusions to be shifted toward tip portion 571 of ejection claw57.

Further, when the prescribed angle θ is smaller than 80°, a sheet tendsto cut into the root 592 a of protrusion 592, and scratches or the liketend to be caused on a contacting portion on the sheet when a bundle ofsheets is ejected.

A length of the protrusion 592 is extended across the total length inthe width direction of ejection claw 57.

The protrusion 592 may be divided in the form of broken lines.

A protrusion located at the uppermost position of the ejection claw 57among plural protrusions arranged on sheet contact section 59 is tallerthan other protrusions.

In other words, protrusion 594 that is taller than protrusion 592 isprovided on the tip portion 571 side.

The protrusion 594 prevents a bundle of sheets or sheets constituting abundle of sheets from being protruded from ejection claw 57.

Therefore, it is preferable that height h2 of the protrusion 594 isabout 0.4 mm, for example, which is higher than height h1 of protrusion592.

Protrusion 594 has an angle of about 120° to the bottom plane of recess595 to prevent protrusion 594 from kicking a trailing edge of a bundleof sheets and from causing damage even when a bundle of sheets is drawnout by paired ejection rollers 20.

In this case, protrusion 594 prevents sheets constituting a bundle ofsheets from being protruded from ejection claw 57, because a bundle ofsheets is caught mechanically by the protrusion 594.

With respect to sheet contact section 59, it is made of a materialhaving a great friction coefficient, such as, for example, rubber, sothat a friction may prevent a bundle of sheets from slipping on sheetcontact surface 591 of the sheet contact section 59, in addition tomechanical catching of a bundle of sheets by the aforesaid protrusion592.

It is also possible to replace only sheet contact section 59 inaccordance with a structure of the apparatus, by separating ejectionclaw 57 into main body section 58 and sheet contact section 59.

Each of FIGS. 6 (a) and 6 (b) is a diagram of another embodiment for theprotrusion provided on an ejection claw.

FIG. 6 (a) shows a second embodiment of the protrusion, and FIG. 6 (b)shows a third embodiment of the protrusion.

In FIG. 6 (a), opposite side 598 of surface 593 facing ejection belt 56of protrusion 596 is cut off obliquely.

Other shapes and dimensions are the same as those of protrusion 592.

By doing this, an angle of the opposite side 598 of surface 593 facingejection belt 56 can be an obtuse angle that is greater than 90°, whichcan lighten damage on a portion of the sheet touching sheet contactsurface 591.

In FIG. 6 (b), opposite side 599 of surface 593 facing ejection belt 56of protrusion 597 is cut off to be in the form of a circular arc.

Other shapes and dimensions are the same as those of protrusion 592.

By doing this, an angle of the opposite side 599 of surface 593 facingejection belt 56 can be a circular arc, which can lighten damage on aportion of the sheet touching sheet contact surface 591.

FIG. 7 is a diagram of the fourth embodiment for a protrusion providedon the ejection claw.

Sheet contact surface 591 of sheet contact section 59 is rough surface600, except protrusion 594 of tip portion 571.

The rough surface 600 is a finely irregular surface like the form ofsandpaper.

Since a sheet is caught by protrusions that form rough surface 600, thesheet is restrained from being shifted on rough surface 600 of ejectionclaw 57A toward tip portion 571, thus, conveyance abnormality for thesheet can be prevented.

It is preferable that the surface roughness of rough surface 600 isabout #80-#180 (Japan Industrial Standards). If the surface is finerthan that, a sheet is hardly caught, resulting in difficult control ofconveyance abnormality.

If the surface is rougher than that, a contact portion of a sheet thatcomes in contact with sheet contact surface 591 is damaged.

Though there has been described an occasion where main body section 58and sheet contact section 59, representing different members from eachother, are separated from each other with respect to ejection claw 57,the main body section 58 and the sheet contact section 59 may also beformed unitedly.

In the case of an ejection claw (not shown) wherein main body section 58and sheet contact section 59 are formed unitedly, plural protrusionsbeing the same as protrusions 592 are provided on a sheet contactsurface where a bundle of sheets comes in contact.

Meanwhile, plural protrusions being the same as protrusions 592 restraina sheet from being shifted on the surface of the ejection claw towardtip portion 571. Therefore, the ejection claw does not always need to beconstituted with a material having a high friction coefficient such as arubber, and it may be constituted with ordinary resin used in apost-processing apparatus.

Owing to this, the number of parts can be reduced, and the number oftypes of materials to be used can be reduced, resulting insimplification of a manufacturing process and a reduction ofmanufacturing costs.

By arranging plural ejection claws which push up and eject plural sheetsstacked on a stacker that stocks sheets temporarily at positionscorresponding to sizes of sheets to be used, and by providing pluralprotrusions which protrude toward a sheet, on a sheet contact surface ofan ejection claw where a sheet comes in contact, it is possible toprovide a highly productive post-processing apparatus wherein noconveyance abnormality is caused when ejecting plural sheets in astacker from the stacker, independently of sheet sizes, and thereliability is improved, then, a production shut-down caused by aninterruption with abnormality is lightened, and to provide an imageforming system having therein the aforesaid post-processing apparatus.

1. A post-processing apparatus comprising: a stacker which stocks asheet temporarily; and an ejection device which ejects a plurality ofsheets from the stacker on which the plurality of sheets have beenstacked, the ejection device comprising: an ejection claw which pushesup the plurality of sheets; and a moving device which moves the ejectionclaw along the stacker, wherein the ejection claw comprises a contactsurface with which the plurality of sheets are brought into contact whenthe ejection claw moves and pushes up the plurality of sheets by themoving device, and the contact surface comprises a plurality ofprotrusions which protrudes toward the plurality of sheets stacked onthe stacker.
 2. The post-processing apparatus of claim 1, wherein theplurality of protrusions extend parallel to a width direction of theplurality of sheets stacked on the stacker.
 3. The post-processingapparatus of claim 2, wherein the ejection claw is fixed to the movingdevice and at least a lateral surface facing the moving device amongboth lateral surfaces of each of the plurality of protrusions makes aprescribed angle with a bottom surface of a recess between the pluralityof protrusions adjacent to each other, the recess being adjacent to thelateral surface.
 4. The post-processing apparatus of claim 1, whereinthe ejection device comprises a plurality of the moving devices arrangedin a direction perpendicular to an ejection direction of the pluralityof sheets stacked on the stacker.
 5. The post-processing apparatus ofclaim 1, wherein a protrusion positioned at an uppermost portion of theejection claw among the plurality of protrusions is taller than anotherprotrusion of the plurality of protrusions.
 6. An image forming systemcomprising: an image forming apparatus which conducts image forming on asheet; and a post-processing apparatus of claim 1 connected to the imageforming apparatus.
 7. The image forming system of claim 6, wherein theimage forming apparatus comprises a selecting device which selects apost-processing operation to be conducted in the post-processingapparatus.
 8. The image forming system of claim 7, wherein each of theimage forming apparatus and the post-processing apparatus comprises aninformation communicating device for communicating information about thepost-processing operation selected by the selecting device.